Roller and breast bar mill



May 2, 1939- c CARRUTHERS ET AL 2,156,619

ROLLER AND BREAST BAR MILL 4 Sheets-Sheet 1 Filed Nov. '7, 1936 Fig;

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ROLLER AND BREAST BAR MILL Filed Nov. '7, 1936 4 Sheets-Sheet 4 A TTDRA/E Y Patented May 2, 1939 UNITED 'STTES RoLLEn AND BREAST BAR. MILL Charles Carruthers and John Rowland Torrance, Bath, England Application November 7, 1936, Serial No. 109,654 In Great Britain February 22, 1936 1 Claim.

The present invention relates to multi-stage roller mills of the rolland bar type, and is directed to regulating the pressure or setting between the different grinding bars and the roll.

Where two or more independent bars are employed particularly in mills such as form the subject matter of our co-pending application Serial No. 109,653 in which three, four or a greater number are used, the bars or some of them being arranged to exert different pressures on the roll, it is of great importance that the ratio of the respective pressures of the bars should remain constant and also that the pressures along each bar should be even, and where the bars are adjusted by means of screws this often involves considerable practical difficulty, since the respective pressures are not directly indicated and great care is necessary to get even adjustment.

Moreover in the construction of multi-bar mills as above described, where such factors as the varying pressures on the bar and size of relief orifice have to be established with due regard to the material to be treated, a method of applying the pressure which is amenable to ready calculation is an important desideratum.

The aim of the present invention is to apply pressure hydraulically by a simple self-contained form of apparatus giving the mill operative an easy means of regulating the pressure exerted on each bar thereby determining the fineness of grinding and the mill output, and. in accordance with the invention a chamber containing a fluid is arranged in such relation to the grinding bars as to enable the pressure thereon to be exerted by the fluid stored in thechamber and a control plunger is provided for varying the fluid pressure in the chamber so as to regulate the bar pressures on the principle of the hydraulic press. Considerable pressures can thus be transmitted to the bars through a static body of fluid under the control of a single manually-operated mechanical device such as a fine pitch screw or a lever, cams or other suitable device.

An alternative method is to establish such pressure by means of a pump, whose operation is checked when the desired pressures have been obtained, or by means of a pump and an adjust able valve leak. The pump method allows of the use of a gas in lieu of liquid.

A particularly useful form of control is one in which a weight or series of weights is applied to the control plunger as with this arrangement the pressure on the bars is maintained constant although wear on the bars may cause an outward movement of the pistons and so change the effective volume of the pressure chamber and this non-contacting settings, e. g., where a bar is held in a fixed non-contacting position by means of a spring acting against the hydraulic pressure, and. where there are contacting and non-contacting settings the wear on the latter being considerably less, the settings will remain approximately correct for a considerable time since the bars which have contacting setting will be automatically moved up.

In the case of multiple bar mills having bars of the same thickness the different pressures between the bars can be obtained by varying the total areas of plungers or the like ranged along the bars, through which such pressures are applied, or these areas may be kept constant and differential pressures obtained by varying the thickness of the respective bars. Alternatively a different number of plungers of the same area may be associated with difierent bars The output of the mill can be varied, without varying the predetermined pressure ratio between the different bars, by operating the single control plunger, and fine adjustment can be readily made available by screw or like operation of the plunger.

The bar or bars may be themselves constructed and arranged as plungers so that the liquid can exert a direct pressure behind them. For example they might be arranged to slide in guides, the contact faces between the bars and their guides being machined and ground to give a liquid-tight action, or appropriate sealing rings may be provided for this purpose. however to operate the bars by means of plungers between which and the bars a relief space is provided for any leakage so that'the risk-of the pressure liquid escaping to the grinding region or regions is obviated or reduced.

In order that the invention may be the more readily'understood reference is hereinafter made to the accompanying drawings in which:

Fig. 1 is a side sectional elevation of one form of multiple bar mill incorporating the invention and Fig. 2 is a front sectional elevation thereof.

Fig. 3 is a front sectional view of a cylinder block used in the said mill and Figs. 4 and 5 are plan and side sectional views respectively of Fig. 3.

Fig. 6 is a diagrammatic front view, and Fig. '7 a sectional end view and Fig. 8 a plan View of a form of mill in which the bars may be given a noncontacting setting in relation to the roller.

Referring to Figs. 1 to 5 a hydraulic box or chamber l havinga number of pressing plungers or rams 2 projecting from the box and bearing on the bars 3 is. provided above the bars. The plungers are arranged along the bar and may be reduced in cross section at the parts bearing on the bars.

One form of pressure producing means con- It is preferred sists of a pressure control plunger 4 which projects into the box and is movable by the manual actuation of a mechanical device such as a screw 5, although a lever, cam, gearing or other mechanism may be substituted for the screw. Since the supply of liquid in the box I is common to all the bar plungers and is under the control of a common regulating plunger the intensity of pressure transmitted to each plunger 2 is dependent upon the difierence in the area of the control plunger and that of the bar plungers 2. The pressures exerted by the bars on the roll and the output of the mill may be varied by rotating the screw 5, and a fine adjustment is thereby permitted to the operative Without affecting the pressure ratio.

Hydraulic packings may be provided to prevent leakage round the bar plungers and the control plunger, but such packings may be dispensed with by providing the plungers and the cylinders with machined and ground contacting faces. The plungers may be circumferentially grooved to enable them to move freely without permitting leakage.

The grinding bars may be guided between separator bars 5, the contacting faces of all the bars being preferably machined and ground so as to prevent the material being ground from exuding between the bars.

The pressure exerted on the bars may be effected through the medium of a spring I which is in compression and serves to move the plunger and compensate for any leakage that may occur from the liquid chamber. The spring also allows the plunger to yield slightly in the event of hard particles finding their way beneath the bars.

The mill described permits of multi-stage grinding and very efficient mixing of the material, but the arrangement of the multiple bars with pressure pockets 8 and a relief passage 9 forms the subject of the said co-pending application Serial No. 109,653 so that no claim is made herein to the arrangement per se.

If desired the pressure box with a manual control for setting up the pressure may be connected up by pipe line connexions to individual boxes for each bar, or to individual boxes for each bar plunger.

Good working has been attained in a mill wherein the plungers, were so distributed and were of such areas, that a pressure of 400 lbs. per square inch on the control plunger sets up a pressure of 2000 lbs. per square inch on the first bar (i. e. that nearest the hopper) on the roll, 1000 lbs. per square inch on the second bar, 1250 lbs. per square inch on the third bar, and 2500 lbs. per square inch on the last bar, and if the thickness of the last bar is reduced the pressure per unit area exerted by that bar on the roll is correspondingly increased. In. such mill four plungers were arranged along the. first bar, and five of the same diameter along a last bar of the thickness of each other bar, whilst four smaller plungers were arranged along the second bar and five plungers of the same diameter along the third bar. Such a layout is shown in Fig. 4.

As shown in Figs. 3 to 5, the liquid chamber may be divided off into several smaller chambers Ill connected by passages 9 but an undivided chamber serves as well. The cylinder block I ll may be built up of sections as shown or. it may be made in one piece.

A pressure indicating or leakage detecting gauge II and filling or replenishing device I2 are indicated in Fig. 2.

A relief space [4 is provided into which any material escaping past the bar plunger walls can enterwith little or no risk of being forced between the bar and its guide into contact with the material to be ground.

We prefer to use multiple cylinders and plungers but we do not exclude an arrangement in which a hydraulic box extends along the whole length of a bar and is sealed hydraulically at its sides and ends and the pressure is applied directly to the top of the bar. Or in another way a uniform pressure distributing member extending the length of the bar may be interposed between the plungers and the bar, or alternatively an elongated piston or plunger could work in a corresponding elongated fluid pressure or hydraulic box and apply pressure directly or indirectly to the bar.

Figs. 6 to 8 show a form of apparatus in which the bars may be adjusted to a non-contacting setting with the roll, the pistons, operated hydraulically, acting at spaced positions along each bar as in the form previously described, but movement of the bars towards the roll being opposed by springs I6 which are compressed by the bars l'l attached to the grinding bars.

The lower portions of the springs I6 rest on the fixed end bars 6*, whilst the bars I1 bear on the springs. As the bars H are attached by the screws ll to the grinding bars-and the latter are acted upon by the bar-like extensions I! of the plungers 2, the springs resist the movement of the bars I! towards the roll when by hydraulic pressure the plungers are forced down towards the roll. If the hydraulic pressure be limited with respect to the resistance offered by the spring, the bars may be brought into close, but non-contacting relationship, with the roll. The attaching member l'l' is shown dovetailed instead of screwed into the last bar as this bar is not sufficiently thick to be conveniently tapped.

What we claim is:

A multi-bar roller and breast mill for grinding fluid materials combining a grinding roll; a plurality of grinding bars axially cooperating therewith; means defining a fluid pressure chamber mounted above said bars, said chamber containing fluid under pressure; piston means extending between each of said bars and said chamber and having their upper ends exposed to the pressure in said chamber for urging the individual bars into grinding relation with said roll; at least certain of said piston means having upper ends of different effective areas whereby the respective bars actuated thereby are urged toward the roll with diiferent pressures in response to the unit pressure of the fluid in said chamber; whereby the relative pressures exerted by all of the bars on the roll is maintained at a predetermined invariable ratio; and means for varying the absolute pressure in said chamber thereby to vary the unit pressure acting on said piston means and hence the aggregate pressure of the bars on said roll while maintaining the ratio of pressures on the respective bars constant.

CHARLES CARRUTHERS. JOHN ROVJLAND TORRANCE. 

